Why are the political parties trying to appease the evangelicals?

It doesn't make sense to me at all. When we occupy another country overseas we try to isolate the extremists and cut them off from having any idealogical appeal with the general population, yet both the democrats and the republicans work hard to try to "woo" these people. Both the parties should be working to isolate them and let them know that the American people will not tolerate their attempts to enforce their extremists views on America.